As, Sb, Be and Ce enrichment in minerals from a metamorphosed Fe-Mn deposit, Val Ferrera, eastern Swiss Alps

Several small syngenetic-exhalative Fe-Mn deposits metamorphosed under blue schist- to greenschist-facies conditions occur in Triassic marbles of the M iddle Penninic nappes in Val Ferrera (eastern Swiss Alps). Pink muscovite - aegirine - hematite albite schists associated with the ores in one of thes e deposits (Starlera mine) contain an unusual assemblage of As-. Sb-, Be-, End REE-rich minerals that developed after the main deformation (D-1). In t hese pink schists, As is present in significant amounts in both titanite (t o 3.46 wt% As2O5) and fluorapatite (to 13.8 wt% As2O5), and is a major comp onent of bergslagite, CaBeAsO4(OH). Antimony is an essential constituent of rutile (to 30.63 wt% Sb2O5), titanite (to 9.55 wt% Sb2O5), and pyrophanite (to 1.91 wt% Sb2O5), in which it is accommodated via the exchange vector S b5+Fe3+Ti-24+. Romeite, (Ca,Na,square)(2)(Sb,Ti)(2)O-6(F,OH,O), is also an important host for Sb, but in addition it incorporates major amounts of REE (to 23.4 wt% Ce2O3). The pink schists at Starlera are the second reported occurrence of natural Sb-rich rutile and Sb-rich titanite (after Praborna, western Italian Alps), and the third of As-bearing titanite (Praborna and W annigletscher, Binntal, central Swiss Alps). The Starlera deposit is furthe r characterized by the presence of thick Veins of romeite-tilasite (CaMgAsO 4F). Mast of these late (post-D-1) veins are closely associated with intens ely foliated pink schists, indicating that they formed from fluids that pas sed through the schists. These fluids must have carried As, Sb, and Ti, and probably were similar to those responsible for growth of the post-D-1 As, Sb, Be, Ti, and REE minerals in the pink schists. The metal content of the fluids was most likely derived from the surrounding ores. The unusual assem blages in both veins and pink schists at Starlera document mobility of As, Sb, Be, Ti, and REE under lower greenschist-facies conditions and in a rela tively oxidizing environment.